OBJECTIVE: To evaluate the influence of prenatal conditions on the development of immune responses during infancy. RESULTS We continue to assess the ways in which different prenatal, pregnancy conditions affect the development of the nervous and immune systems at birth and across the first year of life. We have shown that the maturation of neuromotor responses, as well as the neural substrate underlying emotionality, is sensitive to prenatal factors. Further, we have shown that prenatal experiences can affect the physiological response to cytokines when monkeys are tested as yearlings. FUTURE DIRECTIONS One new approach involves the development of a prenatal vaccination paradigm to evaluate how prenatal conditions influence the efficacy of vaccination against Haemophilus influenzae, the primary bacterial vector that causes meningitis in children. Pregnant monkeys are vaccinated one month before term, and the transplacental transfer of antibody is evaluated in their infants. KEY WORDS infant development, prenatal, Haemophilus influenzae, lymphocyte proliferation, natural killer cell activity